In U.S. Pat. No. 3,110,320, Dr. F. J. Hassler disclosed what was then a new method of curing and drying tobacco. This method was and is now referred to as a bulk curing. Since the advent of bulk tobacco curing by Dr. Hassler, and especially in the last five years, tobacco farmers have mechanized at a very rapid rate. In mechanizing, many farmers have turned to bulk curing as a means to cope with the scarcity of labor and as means to save and minimize labor over conventional tobacco curing techniques.
Bulk tobacco barns being produced by the industry today and used by tobacco farmers are still remarkably similar in basic design to the first commercial barns built and sold. Bulk barns today are generally constructed of a wood frame structure supported by a steel main frame and enclosed by galvanized sheet metal, aluminum, or other suitable type of exterior building material. Also forming a part of such conventional bulk barns is a forced air furnace system, oil or gas, that acts to generally circulate air vertically through the bulk barn and to generally control the temperature level within the structure. These barns are generally referred to as being "portable" as they are usually transported from a manufacturing site to a farm where the barn structure is placed on a concrete slab, the ground, or other type of foundation structure. After being placed on the farm, portable bulk barns are capable of being moved. But due to the nature of the conventional bulk barn design coupled with their size and weight, moving such barns is quite awkward and in fact entails time, labor and special moving equipment. Thus in practice the so called "portable" bulk barns are not routinely moved about by the farmer.
While these conventional bulk barns have generally served the farmers well, many such bulk barns being marketed today operate very inefficiently, have high initial cost and are costly to operate in terms of fuel consumption and electricity usage, and are often less than completely satisfactory in curing and drying the tobacco material within the structure.
In the way of a particular example, due to the type of design and manner of construction, conventional bulk barns tend to leak air. These areas of air leakage occur mostly from pressurized plenum area but can occur in and around the barn wall structure, the roof structure or even about the front and rear ends of the barn. In addition, air leakage may be found where the barn joins and is supported about a pre-set concrete slab or other base support structure. With air leakage from the bulk barn, it is very difficult to maintain acceptable and proper levels of static pressure within the barn structure, especially in the lower plenum area defined underneath the area of the bulk tobacco material within the barn. Insufficient static pressure often results in insufficient air flow uniformly through the tobacco leaf material within the bulk barn, and consequently in such cases one can expect the quality of the final cured and dried tobacco product to be less than satisfactory. This is so because it is fundamental and well known that sufficient air flow must be maintained at all times in order to properly cure and dry bulk tobacco.
Moreover, the very basic design of commercially available bulk barns complicates manufacturing and shipment. In manufacturing, the bulk barns are built by beginning with a steel foundation frame. Next a complete wood frame structure is built on the foundation frame. Thereafter aluminum, galvanized sheet metal of other suitable exterior material is placed on the outside wood frame structure. Obviously such a manufacturing operation includes many parts, components, sub-assemblies and a great deal of labor to perform the various assembling and erection duties that are required. Besides the complexity involved and the inventory required, this type of manufacturing operation in the end is relatively expensive. Furthermore, once manufactured these bulk barns are large, bulky, heavy and quite difficult to handle. Transportation and shipment become time consuming and expensive, and requires very careful handling techniques in order to avoid damage in loading, unloading and in transit.